It's been about 2 years since I installed a Pioneer DVR-108 in my G4 tower at home, but I've been using it ever since to burn piles of CDs and DVDs using Toast, which I keep updated, at the fast speeds described by others here, using various name-brand media.
This setup burns discs much faster than newer Intel and G5 iMacs!
As for updating the firmware, I did do this on the G4. You can use Stuffit from within OS-X to unstuff the Windows installer, and get to the parts inside. It's not a pretty process, but it works. I learned how to do it by Googling. I have the directions archived on a CD and need to dig it out... It may be there is even newer firmware since my last attempt.